As it is known in this specific technical field, for the final quality check, a process of electrical sorting of the semiconductor electronic devices is carried out by executing a testing EWS directly on wafer. To this aim it is often necessary to electrically connect a testing apparatus, called tester ATE, that executes the measures on the devices of the wafer.
This situation is schematically shown in FIG. 1.
Between the apparatus ATE and the wafer 1 there is an interface comprising a probe card 2 having an end 3 (probe head) with which also several hundreds (or thousands) of probes 4 are associated that electrically connect the ATE to the almost totality of the pads of the devices to be tested.
In general the wafer is positioned on a support 5 called chuck belonging to an apparatus called prober.
In consequence, the probes 4 of the ATE should be temporarily connected to all the pads 6 of the electronic device to be tested, as shown in FIG. 2, or of the devices since the testing in parallel of several electronic devices simultaneously is more and more frequent.
The number of probes 4 of the resources necessary for the testing may also be smaller or identical to the number of pads 6 present on the device.
In a similar way checks are carried out also on integrated circuits for which it is necessary to contact the respective bumps.
Within this domain it may be very important that the generic probe 4 is well centred on the corresponding pad 6.
Last generation electronic devices have a very high number of pads to be contacted which have a more and more reduced area and are often very close to each other.
In particular the more a pad has a small size, the more probable the breakage of the passivation surrounding the pad is further to a non correct contact by the relative probe.
It may be very important that all the probes are planar with each other on the vertical axis Z and have a high alignment with respect to the horizontal plane XY. This allows to reduce the damaging problems of the pad and breakages of the passivation.
At present the testing in production of the correct alignment between the generic probe and the pad may be made by observing the signs that the probe leaves on the pad after having contacted it, but this check occurs after having executed the testing step and is not preventive.
FIGS. 3B to 3D show examples of signs left on a pad by the non correct positioning or alignment of a test probe.
The testing operation may, however, be executed on the prober in a manual way or in an automatic way.
Apparatuses also exist that are different from the prober that test the alignment and the planarity of the probes of the probe card.
However, recently, for meeting the growing requests of electronic applications able to sustain higher and higher temperatures, new materials have been introduced for realising the end pads of the electronic circuits and for the connections between these pads and the substrate of the package, which is the container of the circuit, so as to ensure a good electric connection.
Some of these materials for the pads are also used to strengthen the pad itself and in consequence these materials have a greater hardness than the materials traditionally used like the aluminium.
This implies that the signs left by the probe may not always be seen on these particular hard materials, even after different mechanical actions of contacting of the probes on the pads.
In consequence, a check in production of the correct centering of the probes on the pads may become difficult, requiring long times and with consequent breakage problems of the passivation that implies the production performance loss with a consequent economic damage.
The adoption of pads realized with hard metals thus may make it difficult to execute a process of reliable probing and in consequence it is possible to lose production electric performance with a consequent increase of the costs.
Production problems are added to all this, these problems further burdening the costs in case, for example, testing problems of a non-immediate solution arise, such as for example a bad electric contact between the probe and the pad.